The present invention relates to the procedures used for obtaining the deflection of the path of charged particle beams, such as for example, the intense ion beams used in ion implanters.
It is known that heavy ion beams of the same sign, reaching or exceeding a certain density, for example approximately 1 mA/cm.sup.2, are difficult to maintain in the state, in view of the very high repulsive forces exerted between the various particles and which, without special precautions, tend to bring about the splitting of the beam. Such beams can only exist if they have a minimum of space charges of particles with the opposite sign to that of the beam particularly electrons in the case of a beam of positive heavy ions. In general, these electrons are present within the beam, due to the fact that a total vacuum can never be formed in the enclosure in which the beam is displaced and that part of the ionized residual air supplies the necessary electrons.
In order to be able to manipulate such high density, heavy ion beams, it is consequently important not to destroy the compensation by this space charge of particles of the opposite sign, which consequently prevents the use of electrical fields for obtaining deflections of the beam required for the use thereof. Thus, at present, the path of the beam is deflected by magnetic fields, which make it possible to retain the aforementioned compensation, while ensuring an adequate deflection.
Thus, according to the prior art, the beam is deflected by varying the radius of curvature of the path which it follows by creating a zone where the magnetic field varies as a function of time. This is generally brought about by means of a magnetic circuit having an air gap and in which circulates the flux induced by a magnetizing coil, into which is injected the variable intensity current, which produces the variable magnetic field.
All these known deflection processes or apparatus lead to serious disadvantages involving losses by eddy currents and hysteresis in the magnetic material exposed to the variable field, and which are by no means negligible, and the use of a relatively high reactive power during the variation of the magnetic field. As an example of this latter disadvantage, reference can be made to the case of the deflection of a beam of antimony ions of 200 keV with an angle of roughly 1.degree. at 50 Hz. If the magnetized space volume corresponds to an air gap of length approx. 0.2 m, width 0.2 m, air gap thickness 0.1 m, the obtaining of a maximum field of 1000 Gauss or 0.1 Tesla in said air gap leads to the use of a reactive power of approximately 5.8 kVA. A reactive power of this order of magnitude is very prejudicial to the equilibrium of the power supply network from which it is taken.